Yeah but that's just red meat. When they say communists normally they mean standard liberal democrats. If it was actually an "antifa" type person it will be different in response from the government that it will mobilize at all levels against the left. Whereas if it's a liberal the mainstream media and FBI aren't going to call them a communist, they'll say mentally ill or whatever the standard take is and slowly it'll fade away.

Trump does not likely truly believe that Democrats are in league with communists knowingly. After all he voted Democrat for years and donated to them and was close to them. He knows how the sausage is made. That's bullshit culture war red meat fodder for the rubes. He might think they're importing non-whites to destroy America, that's it's vaguely crypto-communist or whatever but I really doubt that an anti-Marxist program is a strong part of his ideology. Being anti-communist is just standard, and it's a convenient foil and boogeyman to rail against. Too many people on the left buy into the liberal histrionics about Trump being Hitler 2.0 which he isn't. He's a reactionary and a grifter and he excites reactionary rubes into violence and that's about it. The American state will take the American people whatever direction it wants with or without him.

It absolutely matters because as much as Trump and such can bray about commies shooting him or whatever (he'll be as likely half the time to say something like "Clinton/Biden crime family" or whatever), the government is only going to do so much based off that.

The threat is not that Trump gets upset at and decides to enact vengeance personally on communists (that is a problem if the person was one and no Trump is again not so brain-melted that he wouldn't understand that a bog standard white male Biden supporter who believed Russiagate is not the same as the image of a pink-haired transgender, anarchist symbol wearing, black bloc type). It's that if they actually are one. Actually are part of DSA or have photos supporting antifa or being part of it or part of some left group, that Trump doesn't have to lift a damn finger. The FBI, Biden admin as mentioned, Dept of justice, Homeland security, NSA, etc, etc will all on their own with finger-point from the permanent part of the state institutions of violence gear up and turn heavily towards the left and further antagonizing it on their own. It will create momentum for more bills at the national and state level to criminalize protesting, left symbols, left speech, etc. Yes you'll get that anyways no matter what but it moves slowly and if it were the case it would push it through more quickly with less even token resistance.

And let's not forget, a large part of the US intelligence state itself tried to slander Trump. They invented Russiagate hoax, they've been saying he'll weaken our security and NATO commitments, all kinds of fearmongering. So if a bog-standard, CIA loving liberal did this based off their propaganda, they can't really do anything but quickly bury it under the label of "mental illness don't look further into it".